Garmin Varia RearVue 820 (bike radar with braking detection): our review

A narrow country road rarely stays neatly organised. Cars move across to pass parked vehicles, bends interrupt the view and a cyclist may already be choosing a line around broken tarmac. The Varia RearVue 820 has a detection angle of 60 °, a broad field that also covers the edges of the lane. That breadth is its most interesting radar characteristic here: the area covered extends beyond a thin strip directly behind the saddle.

Coverage matters alongside distance. For a Sunday morning ride on a rural A-road, that wider field is a useful reason to consider this model. It remains assistance for the rider, however. Manufacturers remind cyclists to stay attentive and look behind before changing position. That matters particularly before moving around a drain cover into the traffic stream, however reassuring the information on your bars might seem.

The rear light is rated at 100 lm, placing it among the brightest rear lights on the stated figures. That output should help catch a driver's eye from behind, although low autumn sunshine and a busy road can still make a cyclist harder to notice. Its job is to help you be seen; illuminating the road belongs to another light.

Would you rather leave the light setting alone when the commute home gets gloomy? The specified mode is steady, which suits riders who favour a continuous rear light. Brake detection is also included. That is a relevant feature for roads where traffic lights, junctions and roundabouts repeatedly interrupt your rhythm. We like the combination of a strong stated output and a straightforward lighting approach. Your handlebars already have enough competing opinions.

A long Saturday route can be followed by several shorter journeys before you remember the accessories hanging on the bike. With stated battery life of 30 h, this radar offers substantial time between charges. That should make regular riding easier to organise, but the figure should not become a promise for a particular route: runtime depends on the operating mode.

The built-in rechargeable battery uses USB-C. A charging time of 2.5 h means allowing a proper pause at a socket, rather than assuming a quick connection while you put your shoes on will replenish it. Plugging it in after cleaning the bike is a more sensible habit than remembering it beside the front door as the club ride departs. For riders juggling commuting and weekend miles, the appeal is less frequent charging without pretending that the battery can be forgotten altogether.

This radar has verified compatibility with a bike computer from Garmin and connects using ANT+. That connection alone does not establish support for every computer. Check your exact receiver before ordering. If the display on your bars already handles navigation and ride information, receiving the radar's information there makes practical sense, provided the pairing is supported.

The mounting position is the seatpost, with round seatposts explicitly supported. On a bike already carrying a saddle bag, consider the available space before committing to another accessory beneath the saddle. The stated ingress protection rating is IPX7, a laboratory classification relevant to wet riding. For autumn rain on the morning commute, weather protection belongs in the buying decision alongside mounting. Manufacturer care guidance is simple: use a dry or slightly damp cloth and keep chemical cleaners, solvents and insect repellent away from the finish.

At 90 g, the RearVue carries a typical weight for a cycling radar. Even so, those grams are our main reservation. Riders who scrutinise every accessory may find the balance less persuasive than the lighting and detection coverage. A radar does not become weightless just because it lives beneath the saddle.

The COOSPO TR70 is better suited to riders who count the grams. At 63.7 g, the alternative saves weight beneath the saddle; its longer stated battery life strengthens the case for riders who prioritise those benefits over brightness and a broader detection field. The COOSPO TR70 has a higher battery life figure of 40 h, appealing if you want longer intervals between charges. The COOSPO TR70 has a lower light output of 70 lm, giving up some stated brightness. The COOSPO TR70 has a lower detection angle of 40 °, covering a narrower field behind the bike. The COOSPO TR70 has a similar overall score.

Our overall assessment puts the Varia RearVue 820 among the best on the site. Choose it for the broad field and bright steady light; choose the alternative when reducing weight and extending battery life matter more.